MC13020P データシートの表示（PDF） - Motorola => Freescale
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MC13020P Datasheet PDF : 6 Pages
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Vcc
“ ,,, ,.
6A 2, ,
0.01
3
+IFe
“
Input
Env
DET
l+L+R
l/cose
+
r
7
Var
Gain
Phase
DET
,
1e
Vco
FIGURE 4 — BLOCK DIAGRAM
1, , “5* ,
20, .
+
+
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4, , 10, ,
4r
9W
——— ——- ___
r
A
I
=
Optional
AGC
To Tuner
Monaural
e!
0
Note 1: Output polarity is
See Text
dsfined for recsiver front
end with L.O. abovs signal
frequency.
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MOTORO~ C-QUAM@ — COMPATIB~~$“1,,
QUADRATURE AM STEREO
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INTRODUCTION
“t:,.:,,$t$~~~,t,i:.,:t,:\?t,t\<,~+~$?$~~,..*~:,,
In C-QUAM@, conventional,, ~~~d$ture amplitude
modulation has been modifie~,~y ~dftipiying each axis
by COSOas ‘shown in ~g~~j~sdfid 3. The resulting
carrier envelope is 1 + L.,+~+,i~~., a correct sum signal
for monaural receiver&a* ”’Forstereo receivers oper-
sting in monaural mod@$y# 25 Hz pilot signal is added
chronously detected by conventional means; The I and
Q detectors are held at 0° and 90° relative demodulation
angles by reference signals from the phase-locked,
divided-down VCO. The output of the I DET is 1 + L+ R,
with the added benefit (over the Env DET) of being able
to produce a negative output on strong co-channel or
noise intetierence. This is used to tell the Lock circuit
to go to monaural operation. The output of the Q DET
is the L– R and pilot information.
to the L-R infor~~,~’n,at a 4% modulation level.
\ ‘t+*,‘<J.$,,*~l,\,*.:..,f’)”
THE DECOQ,~, ::$
The M~~$*
takes the output of the AM IF amplifier
THE VCO
The VCO operates at 8 times the IF input frequency, ~
which ensures that it is out-of-band, even when a 260
kHz IF frequency is used. Typically a 450 kHz IF fre-
and p~~as the complete C-QUAM@ decoding func-
tio~r+~~~,?absence of a good stereo signal, it produces
a@J&,Wgraded monaural output. Note in Figure 4 that
$~$~~+ R information delivered to the output always
‘&mes from the envelope detector (Env DET).
The MC1 3020P decodes the stereo information by
first converting the C-QUAM@ signal to QUAM, and then
. detecting QUAM. The conversion is accomplished by
comparing the output of the Env DET and the I DET in
the Err AMP. This provides the l/cos8 correction factor,
which is then multiplied by the C-QUAM@ incoming sig-
nal in the Var Gain block. Thus, the output of the Var
Gain block is a QUAM signal, which can then be syn-
quency is used with synthesized front ends. This places
the VCO at 3.6 MHz, which permits economic crystal
and ceramic resonators. A crystal VCO is very stable,
but cannot be pulled very far to follow front-end mis-
tuning. Pull-in capability of * 100 Hz at 450 kHz is typical,
and de-Q-ing with a resistor (see Figure 7) can increase
the range only slightly. Therefore, the crystal approach
can only be used with very accurate, stable front-ends,
By comparison, ceramic and L– C VCO circuits offer
pull-in range in the order of *2,5 kHz (at 450 kHz), Ce-
ramic devices accurate enough to avoid trimming ad-
justment can be obtained with a matched capacitor for
Cs (see Figures 1 and 5).
MOTOROLA
Semiconductor Products /nc.
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